1. Field of the Invention
The present invention relates, in general, to a vacuum generating device used for generating negative pressure in an absorption unit, such as an absorption pad, of a vacuum system, such as a vacuum feeding system used on a production line, and, more particularly, to a vacuum generating device fabricated in the form of a so-called xe2x80x9cejector pump stackxe2x80x9d.
2. Description of the Prior Art
An ejector pump stack-type vacuum generating device is a machine that is fabricated by closely arranging a plurality of ejector pump modules having the same shape and construction side by side, and by fixing such arranged ejector pump modules in a casing frame. In such a vacuum generating device of the ejector pump stack type, each of the ejector pump modules is connected to an absorption unit so as to generate negative pressure in the absorption unit. Such an ejector pump stack-type vacuum generating device has been preferably used in a vacuum feeding system to feed a heavy material from one place to another. When one or more absorption units, connected to the ejector pump modules of an ejector pump stack-type vacuum generating device used in a vacuum feeding system, unexpectedly fail to maintain pressure, the remaining normally functioning absorption units steadily maintain their negative pressure to safely hold a target heavy material and feed the material to a desired place.
However, conventional vacuum generating devices of the ejector pump stack type have a complex construction, so that they are expensive and are difficult to use. For example, U.S. Pat. No. 4,861,232 discloses a vacuum generating device that is fabricated in the form of an ejector pump stack. In the US vacuum generating device, a plurality of ejector pump modules, each having a vacuum-on solenoid valve and a vacuum-off solenoid valve on both sides thereof, are sequentially stacked along a fitting rail by securing the fitting bases provided at the bottoms of the pump modules onto the fitting rail, thus forming an ejector pump stack. However, the above-mentioned US device is problematic in that it requires a vacuum-on solenoid valve and a vacuum-off solenoid valve on both sides of each ejector pump module, so that the device has a complex construction, resulting in an increase in the production cost of the device.
Another example of conventional vacuum generating devices fabricated in the form of an ejector pump stack is referred to in a catalogue of PIAB of Sweden (Vacuum Technique 96-35, Page 2:16-2:23). The PIAB""s vacuum generating device is fabricated by closely arranging a plurality of ejector pump modules side by side, and fixing the pump modules in their places inside a casing to form an ejector pump stack. In the PIAB""s vacuum generating device, each ejector pump module must have a compressed air inlet port, so that it is necessary for the device to be provided with the same number of air inlet lines as that of the ejector pump modules of the pump stack, thus resulting in a complex construction of the device and being inconvenient to a user while using the device.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a vacuum generating device which is fabricated in the form of an ejector pump stack with a simple construction, and which is reliably controlled in the vacuum-on operation and vacuum-off operation of its ejector pump modules by a single vacuum-on solenoid valve and a single vacuum-off solenoid valve, thus accomplishing the desired simple construction.
In order to accomplish the above objects, the present invention provides a vacuum generating device, comprising a plurality of ejector pump modules sharing the same shape and construction, and closely arranged side by side while coming into contact with each other, each of the ejector pump modules including an air inlet chamber opened at two opposite sides thereof, a vacuum chamber opened at a single side thereof, and an air outlet chamber opened at two opposite sides thereof, with communicating means formed in each of the ejector pump modules to allow the air inlet chamber, the vacuum chamber and the air outlet chamber of the ejector pump module to communicate with each other, and a vacuum port formed on a side surface of each of the ejector pump modules so as to communicate with the vacuum chamber of the ejector pump module; a casing including a front panel brought into contact with a first of the ejector pump modules, a rear panel brought into contact with a last of the ejector pump modules, and a plurality of spacers extending between the front and rear panels to support the arranged ejector pump modules in the casing, with a first air inlet port formed on either of the front and rear panels to communicate with the air inlet chambers of the ejector pump modules, and an air outlet port formed on at least one of the front and rear panels to communicate with the air outlet chambers of the ejector pump modules; a vacuum-off unit assembled with the casing and comprising a block body including a horizontal part and a vertical part, with a plurality of guide holes formed on the horizontal part along a straight line such that the guide holes are externally connected to a plurality of absorption units and internally communicate with the vacuum ports of the ejector pump modules, respectively, a second air inlet port formed on a surface of the vertical part, a main flow path formed in the vertical part while extending from the second air inlet port, and a plurality of branch paths branching from the main flow path to respectively extend inside the vacuum-off unit to reach the guide holes; and a vacuum-on solenoid valve and a vacuum-off solenoid valve connected to the first and second air inlet ports, respectively, so as to control a flow of compressed air from a compressed air source to the first and second air inlet ports.